1. Field of the Invention
The present invention relates to an optical disc apparatus, and more particularly to the control of movement of an optical pickup.
2. Description of the Related Art
In an optical disc apparatus which irradiates a laser beam onto an optical disc for data recording/reproduction, it is required to accurately move an optical pickup for data writing/reading to a specified position. For example, when an optical disc is loaded or mounted, it is required to accurately move the optical pickup to a predetermined reading start position (hereafter referred to as “rezero position”) so as to read certain data recorded in an innermost circumferential area of the optical disc (such operation being hereafter referred to as “rezero operation”). If a DC motor is used for moving the optical pickup, and a predetermined voltage is applied to the DC motor for a predetermine time to drive the DC motor, so as to move and stop the optical pickup together with a carriage (hereafter referred to as “thread”), then the stop position of the optical pickup is likely to significantly vary depending on the optical disc apparatus, because the load of the moving thread (hereafter referred to as “thread load”) is likely to vary depending on the optical disc apparatus. It may be possible to provide a thread-driving gear with a thread sensor having an encoder, so as to detect the position of the optical pickup and control the movement/stop of the optical pickup, making it possible to accurately stop the optical pickup at a specified position. However, this causes a cost increase due to the thread sensor.
On the other hand, an optical disc apparatus is known which uses a stepping motor for moving an optical pickup so as to detect the position of the optical pickup based on the number of pulses for driving the stepping motor, thereby accurately stopping the optical pickup (refer to e.g. Japanese Laid-open Patent Publication 2000-251270). However, the stepping motor in such optical pickup device has a low torque, so that it is not possible to use the stepping motor in common for moving the optical pickup and for moving a tray of an optical disc. Thus, an additional motor is needed for driving the tray, which causes a cost increase of the optical disc apparatus.
Further, an optical disc apparatus is known which provides, at an innermost circumferential position of an optical disc, a limit switch operated and turned on by an optical pickup. When the optical pickup is moved in a direction directed to the inner circumferential side to turn on the limit switch, the moving direction of the optical pickup is changed to a direction to the outer circumferential side, while a predetermined voltage is applied for a predetermined time to, and thereby drive, a motor for moving the optical pickup, so as to move the optical pickup to a reading position (refer to e.g. Japanese Laid-open Patent Publication Hei 4-241229). However, since this optical disc apparatus does not consider variations of thread loads, it causes variations in the rezero operation.
Similarly, an optical disc apparatus is known which provides, at an innermost circumferential position of an optical disc, a limit switch operated and turned on by an optical pickup. When the optical pickup is moved in a direction directed to the inner circumferential side to turn on the limit switch, the moving direction of the optical pickup is changed to a direction to the outer circumferential side, while a predetermined voltage is applied for a predetermined time to, and thereby drive, a motor for moving the optical pickup. Thereafter, a predetermined reverse voltage is applied to, and thereby brake, the motor (refer to e.g. Japanese Laid-open Patent Publication 2005-332525). If the optical pickup has a low thread load to be easily movable, it absorbs the variations of thread loads, because it enables a strong brake effect. However, if there are significant variations of thread loads, the variations cannot be sufficiently absorbed, causing variations in the rezero operation.